Safety lock for electric switches



NOV. 20, 1934. GETCHELL 1,981,353

SAFETY LOCK FCR ELECTRIC SWITCHES Filed Feb. 6, 1933 20 Benjamin Gets/m1],

\ ORNEY Patented Nov. 2O, 1934 1,981,353 SAFETY LOOK- FOR ELECTRIC swrrcncs Beiijamiri E. Getchell, Plainville, Coma, assignor to The Trumbull Electric Manufacturing. Company, Plainville, Conn., a corporation of Connecticut Application February 6, 1933, Serial No. 655,335 3 Claims. (01. zoo-s7) My invention relates to electrical switches and particularly to the type of disconnecting switches which are used for controlling circuits of high capacity and in which circuits the current is derived from a source in which the power may vary so greatly as, at times to cause the electrical current to greatly exceed the rated or safe current-breaking capacity of the switch.

In certain types of switches, usually made in times provided with an interlocking means for co operationwith the switch to lock the cover closed when the switch is on but which will move or be movedso as to'permit the cover to be opened when the switch is in the off position.

These interlocking means add greatly to the cover latching power of the independent spring catch when the switch is fully closed in the on position but they are often arranged so to move 10 large sizes for controlling power circuits, it is at 86 of the cover directly in the danger zone. If the '35 occur and if the switch is opened under such '40 latches and hinges and directly into the operaaway from the fully latched position as the switch is being opened so that, when the switch contacts have reached the arcing position, the cover latching power of the interlocking means has been so greatly reduced that it'is left for the independent spring latch to bear the brunt of any explosion that may occur within the box.

It has been found in practice however that the combined cover latching power of the independent catch or latch and any usual interlocking means is not great enough to hold the cover closed when the switch is opened under excessive overload conditions, therefore the special object of my invention is to provide a means for also looking the switch mechanism so that the switch cannot be opened while excessive overload conditionsexlst but which will release the operating mechanism so that the switch may be opened as soon as the current has returned to normal conditions or to a predetermined percentage of overload.

Another object is to provide a switch locking means of the character described which is normally inactive but which will automatically operate to lock the switch against opening movement when the current is abnormal or excessive and which will automatically release the switch as soon as the current returns to normal conditions or to a predetermined percentage of overload.

Another object is to provide a magnetically operated switch-locking means which is automatically operated by the circuit to be controlled but which is not directly connected or in series with the circuit.

Another object is to provide a means for locking an electrical switch against opening movement under overload conditions and which means includes a magnet core and an armature for the core, the core and the magnet being so positioned, with respect to the path of the current to be controlled, that the magnetic flux of the current will energize the magnet core and no windings of any description *will be required for the core and no electrical connections to any corelated parts or to the circuit are required for energizing the core.

Another object is to provide a safety locking times extremely dangerous to open the switch when the current is on. Under these conditions the rule is that the switch shall not be opened while the current is fiowing, that is, the circuit must be opened at some other point by means of a circuit breaker of greater capacity before it is safe to open that particular switch.

Notwithstanding the existence of such rules, careless and ignorant individuals may attempt BOJ to open such switches. It is the object of my invention, therefore, to provide means for preventing the openingof the circuit through such a switch while current is flowing in the line.

1 Switches of this type are usually enclosed in 26'. a box having an external operating handle anda cover hinged to the box and, in case of a heavy over-load in the circuit, such switches are extremely dangerous to operate to open the circuit because, the operator naturally stands in front switch is opened under such over-load conditions when the box cover is open, the operator is usually standing in front of the contacts and thus directly in the path of any are or flash that may over-load conditions when the cover is closed, the arc is sometimes so intense as to cause an explosion of sufficient magnitude to blow the cover open or entirely away from its catches,

tors face.

In many instances, operators have been injured and severely burned while opening a switch under such, over-load conditions and, in fact, a

recent instance in which the operator was actually killed, directed attention to the necessity for providing means which would positively prevent the opening movement of the switch under such over-load conditions and thus protect the operator as well as to prevent damage to the switch or other corelated parts.

Boxes for enclosing switches of this type are usually provided-with somesort of an independ ent spring catch or latch for holding the cover closed under normal conditions and are some- M, in,

device which may be readily applied to standard types of switches without material alteration in the general switch construction.

Another object is to provide a safety lock which can be applied to previously installed switches.

Another object is to provide a safety lock of this character which is positive in operation but which is simple and inexpensive.

For the above purposes I have provided an elec-- tromagnetically actuated lock for preventing the opening movement of the switch while the volume of current is greater than can besafely. controlled.

by the switch.

An electro-magnet with a core and aimovable armature is accordingly provided which is' mbunted so as to surround some of the current carrying parts, preferably one of the'hinge posts of the usual knife blade type switch, so that when current is flowing through the post of the switch the resultant magneto-motive force sets up magnetic means and the interlocking mechanism is re-,

leased.

Fig. 1 is a perspective view of one form of construction embodying my improvements and showing the parts in the interlockedlposition.

Fig. 2 is-a fragmentary view showing the parts of theinterlocking mechanism "on a larger scale in a position to allow the switch to opened.

Fig. 3 is a detail sectional view showing the arrangement ofqone of :the electro-magnetic devices.

Fig. 4 is an edge viewof one of 'thexelectro-magnetic devices.

Figs. 5 and 6 are detail views of one form of interlock; j

The drawing shows the invention as applied to a switch for .a three-wire system, having the line terminals 6., 7 and .8- and the load terminals 9, 10 and .11 with "movable switch blades 12., 13 and 14 of the conventicmal hinged Each blade is hinged to a post 15 at its lower end and coac'ts wtth 'a jawmember 16 at its upper end when the circuit is closed. I

Jaws 17 and 18 may be provided "for a suitable fuse or other protective device in each branch of the circuit. In the usual form or construction the .hinge post 15 and accompanying fuse jaw 17 are mounted on a common conducting plate Thev elecimic conducting members above described are all mounted in the usual way-upon an insulating base :20 "is nsually enclosed aboxZl. R

The switch may :be actuated any suitable manner. '.In the dorm shown-the various hinged blades are :corm'ectedsby-an. insulating crossbar 22 and an :oscillating shaft :23 is pivotally supported :at the :oppos'ite sides of the -':box :and connected to the crossbar 22 byzone -or :more links 24. "The switches provided with an external actuatmg handle .25., whose hub 1263s suitably iconnected with the crank shaft 23 in any suitable manner.

A pivoted latch 2'7 is arranged adjacent the shoulder 28 of the hub and is normally held out of engagement by the tension of spring 29.

The latch actuating bar 30 is mounted transversely of the box and adapted to engage the shoulder 31 on the latch 27. This bar 30 is preferably made of non-magnetic material.

The electro-magnet, consisting of the preferably laminated core member 32 and the armature SShin'ged at 34, is mounted to surround the hinge post 15 and the swinging end of the armature '33 is connected at 35 to the bar 30. The magnet is mounted upon an insulating block 36, to which it may besecured by screws 37, or by any suitable rivet means and the block 36 may be secu-r'edior instance, to the plate 19 by screws 38.

It will thus be seen that the bar 30 is supported by the arniatures 33, 33 to reciprocate between the plate 19 and the lower part of the magnet core 32. f

- The adjusting spring 39 is supported in a bushing 40 in the post 15 so that the spring tends to move the armature away from the magnet core or to the leftas viewed in the drawing.

Retractilespring 39 may conveniently be provided with a means to allow for its adjustment in order to operate under predetermined il0lilit conditions- In'the'form shown inFig. 3 the spring bears at one end against the armature and its other end is enclosed in a thimble form of bush ing 40 which is threaded, in screw fashion, into the jaw members 15 of "the hinge =jaws. The closed end of the bushing 40 maybe provided with the usual slot or any other suitable means for turning the bushing to adjust the tension of spring 39. 7

When the switch closed and an overload :occurs, the armatures are drawn up to the respective cores and each armature with its core makes a closed magnetic circuit around the conductor post 15. The magneto-motive force thus gives rise' to lines offorce through the magnetic circuit and to move the armature and to hold theiparts in the closed circuit position with the bar 30 pressing the latch 2 into the path of the projection '28 of the hub 26 to prevent operation of the handle or other-actuating member.

When the overload condition ceases or when.

the numeral; "flowing is normal or less than suincient :to overcome the bias oft'he springs 39, the springs tend to move the armatures so as to retract the locking bar 30 and the spring 29 retracts the latch 27..

Itwlll thus be seen that means is provided for preventing the actuationof the switch except when the circuit-conditions are such that it safe to do so.

Since the operation of my invention depends merely upon the production of magnetic linesof force around a current carrying conductor, it is independentof the character .of the current, which may he either direct .01 alternating, orovided that the -:c.onstructi'on .of electro magnet32 and armature .33 are suited for the iiharacter of flux induced therein, as is *well known :in the ant, and that retractile springs may be suitably adjusted for the tractive force exerted :by the elect-ro-magnet 32, which will :difier with :diffiering types or capacities of currents.

.As certain electrical systems may have whenunitorm values \of current the diffierent conductors thereof, it is .prefierable that at least one electnmmagnet of m l-device he arranged to {be excited by the conductor which carries the greatest value of current, to the end that the switch remain locked when the current in any conductor exceeds the predetermined safe minimum value.

From the foregoing it will be clear that I have provided a safety locking device which is inactive under normal circuit conditions inasmuch as its presence does not in any way affect the usual operation of the switch to which it may me applied, however, when an overload occurs in the circuit, or in any pole of the circuit, the locking device will instantly and positively operate to lock the switch against its opening movement and will retain its switch locking position until the overload period has passed. It will also be clear that I have provided a form of electro-magnet which, together with its method of mounting makes it possible to automatically operate a switch lock in a positive and practical manner and without the usual windings for the core of the magnet and without any direct electrical connection with the circuit to be controlled.

While I have shown and described my switch look as movable to engage a portion of the hub of the operating handle of an enclosed switch of the interlocking type, it is quite clear that the locking bar of my construction may be arranged to lockably engage any portion of any type 0! switch operating handle without departing from the scope of my invention.

I claim:

1. A switch construction including an enclosure having a cover, stationary and movable contacts within said enclosure, external means for operating said movable contacts, a magnet having an armature within said enclosure, a latch operably connected with said armature within said enclosure, said magnet being adapted to move said latch into position to prevent the movement or said external operating means when the current in the circuit is excessive and a spring for normally retaining said latch in inoperable position when the circuit is normal and to automatically move said latch into inoperable position when excessive current conditions have ceased, all of the parts of the magnet, the armature and the latch being inaccessible when the cover is closed.

2. In an enclosed electric switch, a box, a cover for said box, stationary and movable contacts within said box, an external operating handle having a hub supported in a wall of the box and means of connection with the movable contacts to actuate the same, an inaccessible spring retracted latch within said box adapted to engage the hub to prevent the manual operation of the switch under excessive overload conditions, a magnet having an armature within said box adapted to be actuated by current passing through said switch and an inaccessible'rod connected to said armature and adapted to engage said latch to operate the same in opposition to said spring.

3. An enclosed switch including a box having a cover, stationary and movable contacts mounted within the box, an external pivoted actuating handle carried by the box, means of connection betweensaid handle and the movable contacts of the switch whereby the switch may be manually actuated to open and close the circuit, an electro-magnet having an armature adapted to be actuated solely by excessive current flowing through the switch, an inaccessible latch within said box adapted to be actuated by the armature to prevent the manual operation of the switch under excessive overload conditions and spring means for retracting said latch.

BENJAMIN E. GETCHELL. 

